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DC Joe

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Dear All,


I am working on a project where I have UnilogicUnistream MASTER which read/write data from 10 slaves over CPU's 485 port.

I know that Unistream OPLC can be and MASTER and SLAVE at the same time, but I am wondering is this possible over the same 485 communication port?


Example: SCADA is MASTER to OPLC, and OPLC is MASTER to 10 slaves

Example: SCADA(M) --- OPLC(S & M) --- DEVICES in the FIELD (S)


So please can somebody to answer me and explain a little bit?

Do I need maybe one more 485 com module?


Or I can do it somehow over the same com port?


Kind regards,

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  • 1 month later...

Hi DC Joe,


Yes you will need additional RS485 port.

There is no option to have 2 masters on the same BUS.

In this case you will need to add the UAC-02RSC. (This communication module has one RS232 port and one RS485 port).

You will need to use the built in RS485 port for Slave purposes and the addtional port as Master.

Are you sure that the SCADA doesnt support Etherent connection?

If yes then you can set the UniStream as Slave on the Etherent port and Master on the built in RS485 port.

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